The invention relates to a method for providing generational copy control of a digital video signal, the digital video signal comprising content information, first supplemental information and second supplemental information, the first supplemental information being represented by a watermark pattern, the second supplemental information being represented by a control pattern, the method comprising the step of permitting copying of the content information only if a predetermined combination of the first supplemental information and the second supplemental information is present.
The invention further relates to a device for processing a digital video signal (1), the device comprising means (2) for receiving a digital video signal comprising content information, first supplemental information and second supplemental information, the first supplemental information being represented by a watermark pattern, the second supplemental information being represented by a control pattern.
The invention further relates to a device for providing a generational copy control of a digital video signal comprising content information, first supplemental information and second supplemental information, the first supplemental information being represented by a watermark pattern, the device further comprising means for permitting copying of the content information only if a predetermined combination of the first supplemental information and the second supplemental information is present.
The invention further relates to an analog video signal, being converted from a digital video signal, the analog video signal comprising content information, first supplemental information and second supplemental information, the first supplemental information being represented by a watermark pattern, the second supplemental information being represented by a control pattern.
The invention further relates to a digital video signal comprising content information, first supplemental information and second supplemental information, the first supplemental information being represented by a watermark pattern, the second supplemental information being represented by a control pattern.
The functioning of the method can be understood from WO 98/33325 (PHN 16372), which is hereby incorporated by reference. This document discloses a method of transferring content information and supplemental information. The supplemental information is related to the content information, the supplemental information comprises a control pattern and a watermark pattern related to this control pattern. Marking the content information present in the digital video signal is referred to as watermarking. A watermark must be easy to detect, but difficult to erase or modify without serious degradation of the quality of the content information. Generational copy control requires that the copy status of the supplemental information present in the signal can be measured. Based on these statuses it can be decided whether to allow copying of the content information.
The invention has for an object to provide a method for providing generational copy control of a digital video signal in which the generational copy control can still be exerted in the event that the digital video signal is converted into an analog video signal.
The method in accordance with the invention is characterized in that before performing the step of permitting copying of the content information, the method comprises the steps of converting the digital video signal into an analog video signal and adding pseudo-sync pulses to a blanking interval of the analog video signal, the pseudo-sync pulses representing the second supplemental information.
In the digital video signal a control pattern representing the second supplemental information is present. When converting the digital video signal into the analog video signal pseudo-sync pulses are added representing the second supplemental information.
The invention is based on the recognition that most recorders do not record the complete blanking interval of the analog video signal. Hence, when making a copy the pseudo-sync pulses added to the blanking interval are not recorded. Pseudo-sync pulses are different from the normal sync pulses of a conventional video signal. With the term pseudo-sync pulses, pulses, which extend down to a normal sync tip level and peak to peak white level are meant.
By removing the pseudo-sync pulses, the second supplemental information is changed. The status of the second supplemental information can for example be changed into xe2x80x98Copy-No-Morexe2x80x99 when the pseudo-sync pulses are removed. Since permission of copying of the content information is only given if a predetermined combination of the first supplemental information and the second supplemental information is present in the video signal, copying can be prohibited if the second supplemental information has the status xe2x80x98Copy-No-morexe2x80x99. It can be understood that different combinations of statuses can occur and different predetermined combinations of the first supplemental information and the second supplemental information can therefore be defined. The presence or absence of the pseudo-sync pulses can for example indicate the status. Note that also in the event the pseudo-sync pulses are present, more than one status is possible. The possibility of creating different statuses makes generational copy control possible.
By making no change to the active picture area, any potential degradation of video quality is removed. Another significant advantage of this method is that it takes advantage of existing circuitry in a large percentage of the worldwide installed base of analog and digital cable television and direct broadcast satellite set top boxes (STB, also known as IRD, integrated receiver-decoder) to perform this new generational copy control.
It can be understood from U.S. Pat. No. 4,631,603 that adding positive pulse pairs to the blanking interval of the analog video signal can cause an automatic gain control in a videotape recorder to sense an erroneous indication of video signal level and produce a gain correction that results in an unacceptable videotape recording. In this invention a small subset of the pulses, not causing the erroneous automatic gain control, as disclosed in U.S. Pat. No. 4,631,603 can be used in order to perform generational copy control. This has the advantage that so-called set-top boxes (STB""s), utilizing an encoder IC capable of producing these signals, can be used. A significant percentage of STB""s are nowadays controllable in the requisite manner to produce the signals per the previous patent.
The invention further relates to a device for processing a digital video signal.
The invention further relates to a device for providing generational copy control of a digital video signal.
Another device for providing generational copy control of a digital video signal is characterized in that the device further comprises means for creating a low bit rate signal by turning off and on the adding of the pseudo-sync pulses.
By turning off and on the adding of the pseudo-sync pulses a low bit rate signal can be created. This could be used to communicate known copy protection elements such as (encryption) keys or numbers.
Another device for providing generational copy control of a digital video signal is characterized in that the device further comprises a detector for detecting a characteristic of an analog video signal provided from an analog recording device and means for blocking the analog video signal if the detector detects a characteristic of the analog video signal.
As said above, most recorders do not or not properly record the complete blanking interval of the analog video signal. In the event a recorder does record the part of the blanking interval where the pseudo-sync pulses are present, the generational copy control can not be exerted. In order to overcome this drawback, the analog video signal is inspected whether a characteristic of an analog video signal provided from an analog recorder, e.g. a VCR is present. If such a characteristic is detected, copying is prohibited.
Another device for providing generational copy control of a digital video signal is characterized in that the characteristic is a stability status of a time base of the video signal.
An analog VCR signal usually contains to some extent time base instabilities. Various mechanisms exist for detecting these instabilities. One method is to look for perturbations to a horizontal phase lock loop, which exceed a particular threshold characterizing a VCR. If these instabilities are detected, the presence of for example of watermark with a xe2x80x98Copy-No-Morexe2x80x99-status must result in preventing copying of the content. The status of the second supplementary information, represented by the pseudo-sync pulses, is of no importance in that case.
The invention further relates to an analog video signal.
The invention further relates to a digital video signal.